Numerical investigation on the dynamics of a high-performance motorcycle equipped with an innovative hydro-pneumatic suspension system

A hydro-pneumatic suspension system that was recently proposed as a new solution to improve the performance of wheeled road vehicles, particularly motorcycles, is analyzed. The innovative device is primarily based on a hydro-pneumatic spring and a coil spring arranged in series, which generate a strongly non-linear behavior, and in particular a strongly regressive spring rate (i.e. spring rate is reduced with increasing load). This research aims at an initial assessment of the actual benefits and/or drawbacks provided by this device. Because of the strong non-linearities introduced by this suspension device, multibody simulations are an essential tool to do a realistic performance evaluation of such system, as standard linearization techniques would fail to capture the full dynamics. Multibody models are implemented to evaluate the dynamic response of the hydro-pneumatic system as compared to a standard suspension (i.e. linear spring-rate). As a first stage of the research, this work focuses on the in-plane dynamics, and in particular on preliminary simulations of the motorcycle in straight running at constant speed. The load fluctuations on the rear wheel (grip) as well as the velocity of the suspended mass under two different road inputs (comfort) at various speeds are analyzed. Results show that, although the hydro-pneumatic suspension has a higher resonance frequency at static equilibrium, the comfort level with respect to the softer suspension is basically unchanged, while the hydro-pneumatic suspension shows a great potential in terms of reduction in load fluctuations on the rear wheel, thus enhancing grip. Furthermore, the hydro-pneumatic device shows high sensitivity to hydraulic preload.